More than a fifth of violent offences, including rape, which were written off as "no crime" by the three biggest police forces in England and Wales were wrongly classified and should have been pursued, inspectors have found.
Her Majesty's Inspectorate of Constabulary (HMIC) reviewed 90 reports of rape, violence and robbery that officers at the largest force, the Metropolitan Police, had classed as not being a crime, and found 21, or 23.3%, were incorrectly classified.
At West Midlands Police, the second biggest force, 23.9% of no-crime decisions reviewed by inspectors were wrong, while 28.6% were found to be incorrect at the third biggest force - Greater Manchester Police.
The Inspectorate has published individual reports for 21 forces following an interim report in May, which found a fifth of all crimes - equivalent to tens of thousands of offences - could be going unrecorded by police. Reports on the remaining 22 forces will be published in the autumn.
For the Metropolitan Police, where four cases of rape were found to have been wrongly labelled as "no crime", some incidents were dismissed on the basis of a single phone call.
In total, out of 1,428 incidents, 1,169 crimes should have been recorded, and 948, or 81%, actually were.
Among those recorded, 24 were wrongly classified, and 11 were recorded outside the 72-hour limit set out in Government guidelines.
For violent crimes, 128 should have been logged, but only 75 were, and of 106 sexual offences, 65 were. There were 140 burglaries correctly recorded out of 162, and 321 robberies out of 379.
Scotland Yard does not currently include crimes that arise out of its internal disciplinary process in records that are sent to the Home Office, but the inspectors said it should start doing so immediately.
The audit also revealed "a number of incidents with clear and obvious lines of inquiry that were not, according to the incident record, adequately pursued and resulted by staff".
At Greater Manchester Police, the Inspectorate examined 496 incident records and found that 388 crimes should have been recorded, of which 265 - or 68% - were.
West Midlands Police correctly recorded 328 crimes out of 332 - a proportion of 99%.
Of the 328 crimes correctly recorded, 13 were wrongly classified and 10 were recorded outside the 72-hour time limit.
For Greater Manchester Police, of the 265, 10 were wrongly classified and 22 were recorded outside the time restriction.
The force's "no crimes" included 31 rape cases, of which 22 complied with Government guidelines, meaning nine did not.
Inspectors found that "failures were primarily attributed to the interpretation of additional verifiable information, with those victims suffering with mental health (problems), those young of age or (who were) intoxicated more likely to receive a poor service".
"The process for authorising a no-crime for rape is not sufficient and requires attention."